Israel's president warned Monday that Jewish extremists opposed to this summer's pullout from Gaza and part of the West Bank could assassinate Prime Minister Ariel Sharon (search).

President Moshe Katsav (search) issued the warning as settler leaders tried to rein in extremists by issuing a code of conduct for opposing the pullout, and a court extended the detention of a Jewish youth filmed in Gaza stoning a Palestinian who was already unconscious.

As the mid-August start date for the evacuation nears, opponents — many driven by religious beliefs — are readying more extreme measures to try to stop it. Protesters, most of them Orthodox Jewish teenagers, have blocked main highways several times. Police have reported foiling plots to sabotage water and electricity supplies.

An extremist Israeli opponent of concessions to the Palestinians assassinated Prime Minister Yitzhak Rabin (search) in 1995, and Katsav told Army Radio it could happen again.

"They are definitely likely to try and carry out extremist acts ... like killing the prime minister," he said.

Many Orthodox Jews believe no government has the right to relinquish any part of the biblical "promised land," which includes the West Bank and Gaza. Some rabbis who guide the settlers have urged soldiers to disobey orders to take part in the evacuation and are suspected of tacitly endorsing violent opposition.

Katsav urged settler leaders, particularly rabbis, to temper their calls. He said it was likely extremists would misunderstand statements by some rabbis that the pullout endangers Israel's existence.

"Some misguided individuals may come and say 'I need to save the state of Israel because the rabbis say Israel is in danger'," Katsav said.

Rabin's killer, Yigal Amir, cited rabbinical rulings as his justification for shooting the prime minister.

Protests turned violent last week when a small group of extremists took over buildings in Gaza, clashing with security forces and Palestinians. Extremists also scattered spikes and oil on the main Jerusalem-Tel Aviv highway and blocked highway intersections.

In one Gaza incident that raised an outcry, Israeli teens attacked a Palestinian youth, throwing rocks at his head as he lay unconscious and bleeding. TV cameras showed one of the attackers shouting, "let him die."

Shimshon Sitrin, an 18-year-old West Bank resident who is the prime suspect in the case, was brought before a court in the southern Israeli city of Beersheba on Monday, and a judge extended his detention by six days.

Sitrin's father, Shaul, defended his son, telling Army Radio the case was a conspiracy of the Israeli media.

"When a Jew acts in self defense he is called a killer, or they say he is carrying out a lynching. The ones who are carrying out a lynching here are the media, and no one else," he said.

Settler leaders met in Gaza on Monday to draw up the code of conduct for opposition to the pullout. Last week's violence crossed "a red line," said pro-settler lawmaker Effie Eitam, who initiated the charter.

"Attempts to physically harm people, to target roads are unacceptable," Eitam told Israel Radio. "They are forbidden both by the law and by Jewish tradition, and they do not help the struggle."

The code calls on settlers to refrain from "acts of provocation or revenge against Palestinians," the Maariv daily reported.

In another development, a Hamas spokesman said the Islamic group has decided not to join Palestinian leader Mahmoud Abbas's government. Sami Abu Zuhri said the Islamic group made the decision late Monday, turning down an invitation from Abbas.

Israel opposes a role for Hamas in the Palestinian government before it lays down its arms, but Abbas prefers to co-opt the militants rather than confront them.